This invention relates to a power absorbing device which comprises a converter for converting reciprocating motion of pistons of a reciprocating adiabatic expansion engine used for a low-temperature refrigerating machine into rotatory motion, a speed-increasing gear for increasing the speed of the rotatory motion, and an electric generator driven by the speed-increasing gear, and absorbs the energy of the reciprocating motion of the pistons.
Power absorbing devices of this type used for reciprocating adiabatic expansion engines have conventionally been known. Many of these devices, however, are bulky and less than perfect. Those large-sized conventional devices are not suited for use with relatively compact low-temperature refrigerating machines set in many places, such as magnetic-floating train operation systems utilizing superconductivity, for example.
By way of example, liquid helium is used as a refrigerant for the aforementioned low-temperature refrigerating machine. The refrigerant is cooled by adiabatic expansion in the adiabatic expansion engine, and mechanical output or energy equivalent to the amount of heat removed is led out of the refrigerating machine through the pistons of the engine. The refrigerating machine will not be able to enjoy uniform and stable operation unless the mechanical energy is absorbed by any means. The refrigerating machine of this type must, therefore, be provided with a power absorbing device for absorbing the energy of reciprocating motion of the pistons. Generally, in one such prior art device, reciprocating motion of pistons is converted into rotatory motion to rotate a flywheel, and a load is applied to the flywheel. In one conventional method of applying the load, the flywheel is braked electromagnetically. In another method, an electric generator as well as the flywheel is rotated to convert the energy of the rotatory motion into electric power, which is used for operating other equipment or dissipated as Joule heat. Although these methods are effective, they require a bulky flywheel and a large-sized electric generator for efficient power absorption, since the pistons move at a relatively low speed and the resultant rotatory motion is slow. This leads to an increase in size of the refrigerating machine. In order to eliminate such awkwardness, there is proposed a speed-increasing gear which increases the speed of the rotatory motion obtained from the reciprocating motion of the pistons, thereby rotating the power absorbing device at high speed. For this speed-increasing gear, there may be used a cycloidal speed-increasing gear, harmonic drive unit, etc. These devices, however, are large-sized, and require a bulky coupling member for connecting them with other rotating mechanisms, thus failing to provide a compact refrigerating machine. Accordingly, there is a continued demand for the development of compact low-temperature refrigerating machines.